Prior stretching advantageously includes a step of paying out the film from a feed spool, a step of stretching it, and a step of winding the stretched film on a take-up spool or core, ready for subsequent use.
Immediately after being stretched, stretchable film is subject to relaxation which leads, over a period that is substantially equal to 48 hours, to the elastic return force being reduced substantially by 50%.
In French patent application No. 92 10254 published under the No. FR-A-2 695 102, the Applicant describes a method of manufacturing pre-stretched film that is relaxed under the stretching tension, and in European patent application No. 97 401 005.0 published under the No. EP-A1-0 806 284, the Applicant describes a method of manufacturing pre-stretched film that is relaxed under low mechanical tension.
Pre-stretched film of known type is wound on cylindrical cores. The film is paid out from the core and is wrapped, e.g. helically, around a load to form an outer wrapping thereabout.
Unfortunately, pre-stretched stretchable film wound on a core turns out to be particularly fragile. For example, being dropped on the ground runs the risk of creating zones of weakness or holes in the margin of the film. Such zones of weakness or such holes in the margin of the film can start tears while a load is being wrapped, or even worse, while a wrapped load is being handled or transported, with the attendant risk of the load being dislocated.
In addition, when the thickness of a film is not absolutely constant, and the film is wound on a core, in particular a core made of card, then overlap zones are generated at the margins between successive layers that impede proper paying out of the film during wrapping, and this can go as far as causing the film to tear.
U.S. Pat. No. 5,531,393 describes a machine for anticipated stretching of a stretchable film for the purpose of texturing the film to facilitate unwinding. The margins of the film are folded over. Reciprocating horizontal motion of the take-up spool spreads out the resulting extra thickness.
GB-A-2 288 594 describes a device provided with means for winding film on a horizontal axis spool driven with reciprocating motion.
Neither of those two documents describes or suggests forming frustoconical or substantially conical end zones that facilitate unwinding of the film, particularly when it is done manually.